The invention relates to a personal safety device, and particularly, but not exclusively, to a personal safety device for monitoring a wearer of breathing apparatus. The invention also relates to a harness for breathing apparatus which may be used with a personal safety device.
Fire-fighters and other personnel entering hazardous (IDLH—Immediately Dangerous to Life and Health) environments often carry with them a personal safety device, known as a Personal Alert Safety System (PASS) or an Automatic Distress Signal Unit (ADSU).
Such personal safety devices typically comprise a motion sensor that monitors the motion of the wearer and an alarm, for example an audible or visual alarm, that is activated if motion is not detected for a pre-determined period of time. If no motion is detected it may indicate that the wearer is injured or incapacitated and therefore the alarm may alert rescue personnel (other fire-fighters, for example) to the location of the wearer. The device may also be capable of manual activation via a panic button if the wearer becomes distressed.
The design and performance of PASS devices is governed by national regulations and standards which are imposed and regulated by regulatory bodies. For example, in the United States (US), PASS devices must adhere to the standards set out in the National Fire Protection Association 1982 Standard (NFPA1982). Similar standards exist in other jurisdictions, for example, British Standard 10999 (BS10999) in the United Kingdom (UK).
NFPA1982 includes numerous requirements for the robustness of a PASS device and aims to represent the real life conditions that fire-fighters may be exposed to. Two of the conditions addressed in NFPA1982 are:
resistance of the device to being muffled when the wearer is in fallen positions; and
ability of the device to operate when exposed to water.
Both of these conditions have the capability of reducing the sound level being emitted by the device. It must therefore be demonstrated, for compliance with NFPA1982, that in a muffle test and a water drainage test that the sound produced by the device is sufficiently loud even under these conditions.
PASS devices typically comprise one or more sounders each having a piezoelectric transducer. Vibration of the piezoelectric transducer produces sound which may be amplified using resonant cavities or sound chambers. If the outlet to the sound chamber is covered, by any physical means, then the sound level is reduced.
The water drainage test simulates the device being partially covered with water and attempts to cover the sounder(s), or sound chambers, with the most water possible to block the outlet(s) or rest on top of the sounder disc, thereby reducing the sound level. The piezoelectric discs typically used in sounders are flat to allow the piezoelectric material to bend from the horizontal plane. However, this flat surface is ideal for water to rest on and dampen the output level. The surface of the disc can be treated to reduce the surface tension, thus causing water to bead and run off the surface. Further, surfaces that are angled to allow water to run off are often deployed and the use of multiple sounders at suitable angles allow for this.
In the muffle test, the device must still meet the minimum sound level when the wearer is in each of the following five positions:
1. Face down with arms fully extended out to the sides;
2. Supine left as far as possible, arms down along sides;
3. Supine right as far as possible, arms down along sides;
4. Foetal, knees drawn to chest as far as possible, arms around legs, and lying on right side; and
5. Foetal, knees drawn to chest as far as possible, arms around legs, and lying on left side.
These positions simulate a fallen fire-fighter, where the device (i.e. the outlet of the sounder) may be muffled by the turn-out gear of the fire-fighter.
To satisfy this test, more than one sounder is typically used so that if the outlet of one sounder becomes blocked, the other sounder(s) will be free to function properly.
For sounders that are deployed on the fire-fighter's back (for example, on breathing apparatus), this is less of a problem as they can be mounted at points that do not come into contact with the fire-fighter's turn-out gear. However, when the sounders are mounted on the shoulder straps or waist straps, the outlets are particularly close to the turn-out jacket.
It is therefore desirable to provide a personal safety device which has an improved sounder arrangement which allows it to be mounted on a shoulder or waist strap.